In many wireless networks, for example networks in the IEEE 802.11 family of protocols and associated chipsets, both uplink transmissions (transmissions from a local unit to a central access point) and downlink transmissions (transmissions from the access point to the local unit) are sent over the same channel. “Channel” may be a frequency channel or a time slot in a time-slotted system. The access point has an omni-directional antenna that covers the local units around it. The local units generally have low-gain antennas and are placed close to the ground, while the access points have high-gain antennas and are elevated above the ground. Collisions between transmissions to and from an access point and the local units it covers are avoided in a distributed way with carrier sense multiple access with collision avoidance (CSMA/CA.). In a large network with multiple access points, there may be interference and contention for access to a channel between transmissions in neighboring access points. Such interference and contention can be mitigated by selecting orthogonal (non-overlapping) channels in neighboring access points, but as networks get larger, eventually channels must be reused.